1. Field of the Invention
The present invention relates to heat pumps and more particularly to adjusting the effective charge of refrigerant in a heat pump system.
2. Background Art
Conventional heat pump systems generally employ a motor driven compressor for compressing refrigerant, a reversing valve for reversing the direction of refrigerant flow, two heat exchangers, either of which may function as a condenser or evaporator depending on the direction of refrigerant flow therethrough, an expansion device for controlling the flow of refrigerant into the evaporator, and an accumulator located on the low pressure, suction side of the compressor to trap incompressible liquid refrigerant slugs which could potentially damage components of the compressor. The heat exchangers are disposed in indoor and outdoor locations. Actuation of the reversing valve reverses the function of the heat exchangers, permitting the indoor heat exchanger to function as the evaporator for summertime cooling or as the condenser for wintertime heating, with the outdoor heat exchanger performing opposite functions.
Generally, it has been recognized in the art that optimum operation of a heat pump system during the cooling cycle requires a greater effective refrigerant charge than is required during the heating cycle. Because of the differing mass flow characteristics of refrigerant charge between the cooling and heating modes of the heat pump (i.e., a reduced amount of refrigerant charge is required during the heating mode), it is advantageous to include a holding area for the liquid refrigerant in excess of that required by the system. The holding area stores excess liquid refrigerant charge which otherwise might occupy a portion of the condenser during operation of the heating mode. Removing and storing excess liquid refrigerant allows for the use of a higher refrigerant charge during the cooling mode without causing excessive pressure build up in the condenser during the heating mode, thus resulting in increased cooling and heating efficiency.
Prior art methods used to compensate for the increased amount of refrigerant charge required during the cooling mode versus the heating mode are primarily directed to the inclusion of a fluid refrigerant receiver. The receiver inlet is generally disposed on the high pressure side of the expansion valve (with respect to the heating mode). During operation of the heating mode, high pressure fluid refrigerant is allowed to accumulate in the receiver. During the cooling mode, the liquid refrigerant is reintroduced into the refrigerant system as dictated by operating conditions.
A disadvantage associated with prior art systems employing a receiver to remove excess refrigerant is that they generally require a relatively large, high pressure reservoir and usually necessitate utilization of complex and expensive circuitry and valving schemes, which increase both capital costs and maintenance costs.
Another disadvantage associated with prior art systems relates to difficulties in adjusting the amount of liquid refrigerant to be removed from the system during the heating mode. Such systems remove an amount of liquid refrigerant equalling the volume of the receiver. The volume of the receiver is predetermined and if it is later desired to remove a lesser or greater amount of liquid refrigerant from the system, the effective volume of the receiver must be adjusted accordingly.
The prior art lacks a charge balance device for a heat pump system which removes and stores excess liquid refrigerant in a low pressure reservoir without employing complex and expensive circuitry and valving schemes, particularly one which may be easily and inexpensively installed into existing conventional heat pump systems.